The present invention relates to a method for producing a substrate such as a semiconductor on insulator (SeOI) substrate and the substrates obtained according to the method.
One field of application of the invention is that of the methods for producing such SeOI structures, such as Silicon On Insulator (SOI) structures, these structures acting as substrates for producing components for electronics, optics or optoelectronics. Such SeOI structures comprise an insulating layer inserted between a thin layer of semiconductor material and a support substrate. These SeOI structures are generally obtained by transfer of a layer of semiconductor material onto a support substrate from a donor substrate and by then removing a part of the layer of semiconductor material to form the thin layer.
The step of removing a part of the layer of semiconductor material to form the thin layer can be performed by different methods. This removal step is preferably obtained by means of the well known SMARTCUT(® method. Further details concerning this SMARTCUT(® method, which is known per se to the skilled person, can be found, for example, in the article by G. Celler, Frontiers of Silicon-on-Insulator, Journal of Applied Physics, Vol. 93, no. 9, May 1, 2003, pages 4955-4978).
Producing a SeOI structure using the Smart Cut(® method in particular requires a finishing step after formation of the thin layer in order to eliminate the residual roughness of the upper surface of the thin layer. Indeed, when the thin layer is formed, thermal and mechanical treatment leading to detachment of a part of the layer of semiconductor material result in a residual roughness of about 40 to 100 A RMS on the upper surface of the thin layer and formation of a damaged zone over a thickness of a few hundred to a few thousand Angstroms. In this damaged zone, the crystalline quality has been disturbed and damaged by the ion implantation step, close to the fracture plane.
This finishing step generally consists in a light abrasion, polishing, a sacrificial oxidation step on the upper surface of the thin layer, or a combination of these steps to eliminate this damaged zone and restore a surface quality, i.e. a satisfactory roughness. U.S. Pat. No. 6,903,032 describes one such finishing step which comprises a first abrasion step, preferably by sacrificial oxidation, followed by short annealing of the substrate.
Annealing of the substrate at high temperatures cannot be applied to all types of material and in particular is not usable on Germanium (Ge) substrates, or on all types of composite materials or heterostructures such as silicon on a quartz wafer. Performing annealing at high temperatures does in fact result in thermal expansion differences of the different materials constituting the substrate. These thermal expansion differences may lead to breaking of the substrate.
U.S. Pat. No. 6,103,599 is also known for disclosing a method for performing finishing of the upper surface of a substrate. This method consists in implanting hydrogen species via the upper surface of the substrate to form a layer called the implanted layer and in then removing the implanted layer by any suitable means. This type of method presents the drawback of procuring an insufficient reduction of the residual roughness of the upper surface of the thin layer so that this type of method is not used commercially.
Thus, there is a need for improved SEOI structures and methods of making them.